Обсуждение: making queries more effecient

Hi. I have this query that I have been trying to reduce to a single
statement, but haven't figured out how. Am I missing something?

CREATE TEMP TABLE temp20561149207391 AS SELECT DISTINCT ON ("VisitorID")
"VisitorID","Type" FROM "ProgramEvent" WHERE "ProgramID" = 10 ORDER BY
"VisitorID","Created" DESC;INSERT INTO "VisitorPointer839" ("VisitorID")
SELECT temp20561149207391."VisitorID" FROM temp20561149207391  WHERE
temp20561149207391."Type" = 0


Thanks

This should be all you need.

insert into VisitorPointer839 ("VisitorID")
select VisitorID
from ProgramEvent
Where ProgramID = 10
and Type = 0
group by VisitorID

You dont need order by because its not important the order it goes in the
database, just the order that it comes out.
I have found that group by works faster than distinct in some cases.  You
may have to test it for your senario.

Thanks
Chad

----- Original Message -----
From: "Peter T. Brown" <peter@memeticsystems.com>
To: <pgsql-sql@postgresql.org>
Sent: Friday, November 01, 2002 3:24 PM
Subject: [SQL] making queries more effecient


> Hi. I have this query that I have been trying to reduce to a single
> statement, but haven't figured out how. Am I missing something?
>
> CREATE TEMP TABLE temp20561149207391 AS SELECT DISTINCT ON ("VisitorID")
> "VisitorID","Type" FROM "ProgramEvent" WHERE "ProgramID" = 10 ORDER BY
> "VisitorID","Created" DESC;INSERT INTO "VisitorPointer839" ("VisitorID")
> SELECT temp20561149207391."VisitorID" FROM temp20561149207391  WHERE
> temp20561149207391."Type" = 0
>
>
> Thanks
>
>
> ---------------------------(end of broadcast)---------------------------
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>

Peter,

For the rest of our sakes, in the future, please format your SQL before
posting it to request help.

> CREATE TEMP TABLE temp20561149207391 AS SELECT DISTINCT ON ("VisitorID")
> "VisitorID","Type" FROM "ProgramEvent" WHERE "ProgramID" = 10 ORDER BY
> "VisitorID","Created" DESC;INSERT INTO "VisitorPointer839" ("VisitorID")
> SELECT temp20561149207391."VisitorID" FROM temp20561149207391  WHERE
> temp20561149207391."Type" = 0

Can be re-written as:

INSERT INTO "VisitorPointer839" ("VisitorID")
SELECT "VisitorID" FROM (SELECT DISTINCT ON ("VisitorID") "VisitorID","Type" FROM "ProgramEvent" WHERE "ProgramID" = 10
ORDERBY "VisitorID","Created" DESC ) v_first 
WHERE v_first."Type" = 0;

Please also keep in mind that the SELECT DISTINCT ON syntax is a
PostgreSQL-specific extension and is not portable.

--
-Josh BerkusAglio Database SolutionsSan Francisco

Chad,

> Im not sure I can get my head around the difference between doing your
> subselect....
>
> INSERT INTO "VisitorPointer839" ("VisitorID")
> SELECT "VisitorID" FROM (
> SELECT DISTINCT ON ("VisitorID") "VisitorID","Type"
> FROM "ProgramEvent" WHERE "ProgramID" = 10
> ORDER BY "VisitorID","Created" DESC ) v_first
> WHERE v_first."Type" = 0;

This gives him a list of all Visitor IDs where the most recent instance of
that VisitorID is of Type = 0;  It's the equivalent of, in SQL-92:
INSERT INTO "VisitorPointer839" ("VisitorID")
SELECT "VisitorID" FROM "ProgramEvent" pe1 WHERE EXISTS(
SELECT "VisitorID", MAX("Created")
FROM "ProgramEvent" pe2 WHERE "ProgramID" = 10
GROUP BY "VisitorID"
HAVING pe2."VisitorID" =  pe1."VisitorID"AND MAX(pe2."Created") = pe1."Created") v_firstAND "Type" = 0;

... which is what I would use, as I dislike database-specific extensions of
ANSI SQL.

> And Just writing it out straight.
>
> insert into VisitorPointer839 ("VisitorID")
> select VisitorID
> from ProgramEvent
> Where ProgramID = 10
> and Type = 0
> group by VisitorID

This just gives him a list of all VisitorIDs with a Type = 0, most recent or
not.

> Thanks
> Chad "I wanna be Josh when i grow up" Thompson

<grin> Thanks.   But heck, I'm only 32!  I'm not grown up yet!

--
-Josh BerkusAglio Database SolutionsSan Francisco